Leaking tanks and, in particular, leaking underground fuel storage tanks presently pose a significant economic and environmental problem. There are thousands of underground fuel storage tanks in use in service stations and the like throughout the world and, over a period of time, leaks inevitably will occur in many of these tanks. Each leak permits the stored hydrocarbons (fuel) to flow into the ground and into the surrounding environment. Even small leaks are unacceptable since over a period of time, a small leak can contaminate a large area and render it unfit for habitation--particularly if it is a residential area. A leak can also allow ground water to flow into a tank and render the stored fuel unfit for further use. Leaks can also provoke litigation by damaged parties and can result in sizeable damage awards against the owners/operators of the premises on which the leaking tank is situated. Thus, it is most desirable that tank leaks be prevented and/or detected as soon as possible so that the necessary corrective measures can be taken. The problem is of such significance that the Environmental Protection Agency (EPA) has recently proposed that underground fuel tanks of a proposed date of installation be replaced within ten years. While all tanks have a limited life, a high quality properly installed tank can be expected to last far longer than ten years. Therefore, while the EPA rule might perhaps reduce leakage from some tanks, the rule unfortunately lumps high quality and low quality tank installations together. This penalizes the owner/operators of high quality well maintained tanks installation by requiring them to abide by the rules and regulations that should be applicable only to low quality installations.
The industry is aware of the problem of leaking underground fuel storage tanks and for the most part, is using the best possible available apparatus to test the tanks currently in use. However, none of this apparatus is ideal. The ideal tank testing apparatus should meet five prerequisites. These are (1) the apparatus should be of sufficient accuracy to measure the extremely small leakage rates that are required for a tank to meet today's environmental standards, (2) the apparatus must be easy to use so that it can be installed and operated by relatively unskilled personnel as opposed to the use of laboratory level technicians, (3) the operation of the apparatus should not interfere with the normal operation of the filling station or facility of which the tested tank is a part, (4) the results of the test should not be subject to fraud or manipulation by anyone wishing to alter test results, and (5) it is also of great importance to eliminate any operator adjustments or operator interpretation which could cause errors as to how the tank is behaving.
It is necessary that the leak detection apparatus be extremely sensitive (it can detect leaks in the range of 0.02 gallons per hour or less) so that very slight leakages can be detected in a relatively short period of time. It is extremely difficult to detect the loss (or gain) of 0.02 gallons of liquid per hour in a storage tank capable of storing 10,000 gallons or more. For example, in a nine foot diameter tank twenty-one feet long that is half full, the removal of one gallon of gasoline lowers the fluid level 0.00629 inches. The loss of 0.02 gallons per hour would cause a fluid level drop of 0.0001257 inches or 125.7 micro inches per hour. It is difficult to measure changes in fluid level of this magnitude. Also, even when such a change in the liquid level can be accurately and reliably measured, the change may be due to other factors such as a change in fluid density, water table, vapor pockets, vibration, atmospheric pressure, etc. or a change in temperature or by evaporation. This requires that the measurement apparatus, detect and compensate for the level changes caused by these other factors.
Many of the currently available tank testing devices, while reasonably sensitive and accurate, are complex and require the skills of laboratory level technicians in their operation. This precludes the use of relatively unskilled personnel and increases testing costs. Also, many of the currently available testing devices require the placement of apparatus immediately above the fill pipe area of the tank that is to be tested. This is disadvantageous. Tank fill pipes are often situated in the filling station areas that are used by customers during the normal operation of the station. The testing of a tank with apparatus positioned above the fill pipe area requires that portion of the filling station to be shut down and made unavailable to the users of the station. Further, the tank under testing has to be out of service during the testing period. This, causes a loss of revenue to the tank owners. And finally, some methods require the tank to be completely full of product (at great expense to the owner) many hours before the start of testing. Other methods require that the tank be emptied. Some even require the tank to be pressurized. This could damage the tank and create a leak by the test procedure itself--certainly if the test was preformed many times over the life of the tank.
Even if apparatus could be found that meets all of the above mentioned prerequisites, the apparatus would be ineffective if provisions are not made for safeguarding the integrity of the test data. In other words, there may be instances in which persons may wish to alter the test results to conceal the fact that a tank is leaking. Obviously, the purposes of the test are subverted if the integrity of the test results is not protected.
Also, the manual logging of any test data by a technician attempting to read/observed minute changes on their instrumentation is not desirable. Many of the known prior art arrangements generate tank leakage information at the test site wherein the data is read and/or recorded manually by the technician for further use. This is most undesirable due to the inherent reliance of human interpretation of the data derived by such instrumentation. Prior systems may record leakage data, but they are inherently incapable of acquiring accurate data because of the need of interpreting the acquired data and are therefore completely ineffective as a leak detection device. Prior methods and apparatus require manual recording and interpretation of tank leakage data on the spot. Since the information is manually recorded, it is subject to alteration or human reinterpretation by persons who might knowingly or unintentionally conceal the fact that a tank is leaking.
It may therefore be seen that it is a problem in the art to provide tank testing equipment that is accurate in its operation, that can be operated by relatively unskilled personnel, that does not require human interpretation or recording, that does not interfere with the normal operation of the filling station including the pumping of the tested tank, and that provides for the safekeeping of the test results so as to prevent their alteration either by compromise or by human error.